1. Field of the Invention
The present invention relates to a video camera surveillance system, and, more particularly, to methods of image processing for a video camera surveillance system.
2. Description of the Related Art
Video surveillance systems are used to monitor public spaces, such as train stations, market places, street intersections, or the like, and public buildings, such as libraries, agencies, courtrooms, prisons, etc. Video surveillance systems are also used in the private sector, e.g. as alarm systems or for watching over individuals who require attention.
There are numerous known video surveillance systems which may be used to track a moving object such as a person or vehicle. Video surveillance systems usually include a plurality of permanently installed cameras which observe the relevant areas in the surroundings, and they include a possibility for evaluating the video sequences that were recorded using the cameras.
While the evaluation was previously carried out by monitoring personnel, automatic evaluation of the video sequences has become more common. In a typical application of automatic monitoring, in a first step, moving objects are separated from the essentially stationary background in the scene (object segmentation), they are tracked over time (object tracking), and, if relevant movement or patterns of movement take place, an alarm is triggered. One possible design of automatic monitoring of this type is described, e.g., in EP 0710927 B1 which discusses a method for the object-oriented detection of moving objects.
Such video surveillance systems may be referred to as closed circuit television (CCTV). Some such systems utilize a fixed camera having a stationary field of view (FOV). To fully cover a given surveillance site with a fixed camera system, however, it will oftentimes be necessary to use a significant number of fixed cameras.
Movable cameras which may pan, tilt and/or zoom may also be used to track objects. The use of a PTZ (pan, tilt, zoom) camera system will typically reduce the number of cameras required for a given surveillance site and also thereby reduce the number and cost of the video feeds and system integration hardware such as multiplexers and switchers associated therewith. The camera may pan by rotating about a vertical axis, tilt by pivoting about a horizontal axis, and zoom by enlarging or reducing its FOV. Control signals for directing the pan, tilt, zoom movements typically originate from a human operator via a joystick or from an automated video tracking system.
A problem with such a PTZ camera is that despite being able to pan and tilt in almost any direction, the camera has a limited field of view (FOV) at any given moment in time, and thus may not be able to sense all of the motion that surrounds the camera from all directions.
What is neither disclosed nor suggested by the prior art is an improved system and an improved method for sensing motion within a larger FOV and automatically tracking an object that is a source of the motion.